Transparent substrate for mask blank and mask blank

ABSTRACT

In a transparent substrate for a mask blank, which is required to have a predetermined optical characteristic, a substrate mark is formed by cutting off a predetermined corner portion into an oblique section. The shape of the mark is determined in accordance with the optical characteristic of he substrate.

This is a divisional of application Ser. No. 11/224,087 filed Sep. 13,2005. The entire disclosure(s) of the prior application(s), applicationSer. No. 11/224,087 is considered part of the disclosure of theaccompanying divisional application and is hereby incorporated byreference.

This application claims priority to prior Japanese patent application JP2004-265699, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to a transparent substrate for a mask blank and amask blank and, more specifically, to a transparent substrate for a maskblank and a mask blank which are capable of preventing deviation fromspecification with respect to an optical characteristic of the maskblank by assuring an optical characteristic of the transparent substrateor a thin film.

Proposal has been made of a transparent substrate or a mask blank whichis characterized by a specially designed shape of a corner portion ofthe transparent substrate or a specially designed shape of a peripheralportion of a thin film formed on the transparent substrate (for example,see Japanese Examined Utility Model Application Publication (JP-Y) No.63-8900 (patent document 1), Japanese Unexamined Patent ApplicationPublication (JP-A) No. 2000-356849 (patent document 2), JapaneseUnexamined Utility Model Application Publication (JP-U) No. 60-39047(patent document 3).

The patent document 1 discloses a transparent substrate having asubstrate mark formed on the corner portion in order to discriminate amaterial of the transparent substrate.

The patent document 2 discloses forming a substrate mark having anasymmetrical shape with respect to a diagonal line in order todiscriminate many types of transparent substrates.

The patent document 3 discloses uniformly forming a light shielding film(an opaque film) on a transparent substrate except for a peripheralportion and a side surface. With this structure, during use of the maskblank, the light shielding film is not peeled from the peripheralportion and the side surface. It is therefore possible to prevent apattern defect caused by dust generation.

However, each of the substrate marks disclosed in the patent documents 1and 2 has only a function for discriminating the material of thetransparent substrate while an uncoated portion without the lightshielding film disclosed in the patent document 3 has only a functionfor preventing the dust generation from the mask blank.

On the other hand, recently, following miniaturization of asemiconductor device, the wavelength of an exposure light source to beused has been progressively shortened. Specifically, the exposurewavelength has reached 200 nm or less. For example, as such an exposurelight source, use is made of an ArF excimer laser (wavelength of 193nm), an F2 excimer laser (wavelength of 157 nm) or the like. Rapiddevelopment is made of a light shielding film for shielding light forthese exposure light wavelengths or a phase shift film for shifting aphase of the light. As those films, a wide variety of film materialshave been proposed (for example, see Japanese Unexamined PatentApplication Publication (JP-A) No. 2002-162727 (patent document 4) andJapanese Unexamined Patent Application Publication (JP-A) No.2003-280168(patent document 5)).

Further, several proposals are made of a manufacturing method capable ofsuppressing variation in optical characteristic (for example,transmittance or phase difference), which is expected to cause problemsupon forming these films (for example, see Japanese Unexamined PatentApplication Publication (JP-A) No. 2002-90978 (patent documents 6)).Thus, at present, the variation of the optical characteristic of thefilms has been considerably suppressed.

However, when the optical characteristics (transmittance, reflectance orthe like) of manufactured mask blanks were measured, those mask blankswhich do not satisfy the specification with respect to the variation ofthe optical characteristics encounter problems at a certain ratio.

The present inventor has investigated the cause of the above-mentionedproblem from various viewpoints. As a consequence, it has been found outthat the variation of the transmittance is caused by absorption of thetransparent substrate itself for the exposure light, whichconventionally caused no problem.

Recently, a synthetic quartz glass is used as a substrate material of amask blank for use with, as the exposure light source, the ArF excimerlaser which has been rapidly developed at present. The synthetic quartzglass is also used as a substrate material of a mask blank for use with,as the exposure light source, the KrF excimer laser which is practicallyused at present. The exposure wavelength of the KrF excimer is 248 nm.Therefore, even if the synthetic quartz glass has production variation,the transmittance (the transmittance in a plate thickness direction) is88% or higher (wavelength A 240 nm) for a 6025 size (thickness of 6.35mm). Thus, no problems are caused.

However, if the wavelength of the exposure light source becomes shortlike in the ArF excimer laser (wavelength of 193 nm), the transmittance(the transmittance in the plate thickness direction) is sometimes 88% orlower for the 6025 size (thickness of 6.35 mm) because of the absorptionof the substrate itself for the exposure light due to the productionvariation or the like of the synthetic quartz glass. Such reduction ofthe transmittance becomes remarkable in case where the exposure lighthas the wavelength of 200 nm or less (in particular,140 nm to 200 nm).

In the present status, the production variation upon forming the thinfilm is not completely eliminated. As mentioned above, those maskblanks, which do not satisfy the specification with respect to thevariation of the optical characteristic, are considered to deviate fromthe specification by a synergistic effect of the variation of thetransmittance of the substrate material and the variation of the opticalcharacteristic of the thin film.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a transparentsubstrate for a mask blank and a mask blank which are capable ofpreventing deviation from specification with respect to an opticalcharacteristic of the mask blank by assuring an optical characteristicof the transparent substrate and a thin film.

To achieve the above-mentioned object, this invention provides atransparent substrate for a mask blank, which is required to have apredetermined optical characteristic and which is provided with asubstrate mark formed by cutting off a predetermined corner portion intoan oblique section and having a shape determined in accordance with theoptical characteristic.

With this structure, the optical characteristic of the transparentsubstrate can be assured by the substrate mark. Thus, it is possible tosolve such a problem that the mask blank deviated from specification dueto the optical characteristic of the transparent substrate ismanufactured.

Further, in the transparent substrate for a mask blank according to thisinvention, the substrate mark is formed by combining a plurality ofoblique sections.

With this structure, it is possible to increase a number of types of thesubstrate mark and to assure the optical characteristic of thetransparent substrate in detail.

Further, in the transparent substrate for the mask blank according tothis invention, the optical characteristic is transmittance for anexposure wavelength and/or variation of transmittance in a substrateplane.

With this structure, it is possible to assure the transmittance for theexposure wavelength or the variation of the transmittance in thesubstrate plane and to prevent the deviation from the specificationcaused by the absorption of the exposure light by the transparentsubstrate itself.

Further, in the transparent substrate for a mask blank according to thisinvention, the exposure wavelength falls within a range between 140 nmand 200 nm.

With this structure, in a short wavelength region between 140 nm and 200nm in which large variation of transmittance is caused due to thematerial of the transparent substrate, it is possible to assure theoptical characteristic of the transparent substrate for a mask blank.

Further, in the transparent substrate for a mask blank according to thisinvention, a material of the transparent substrate is a synthetic quartzglass.

With this structure, even in the synthetic quartz glass in which thevariation of the optical characteristic occurs due to productionvariation, it is possible to assure the optical characteristic of thetransparent substrate for a mask blank.

Further, a mask blank according to this invention comprises atransparent substrate and a thin film formed on a principal surface ofthe transparent substrate, which is processed to become a mask pattern.The mask blank is provided with a substrate mark, which is formed bycutting off a predetermined corner portion of the transparent substrateinto an oblique section and which has a shape determined in accordancewith an optical characteristic of the transparent substrate, and a filmmark which is formed on a peripheral portion of the thin film and whichhas a shape determined in accordance with an optical characteristic ofthe thin film.

With this structure, it is possible not only to assure the opticalcharacteristic of the transparent substrate but also to assure theoptical characteristic of the thin film. Thus, it is possible to preventthe deviation from specification by a synergistic effect thereof.

Further, in the mask blank according to this invention, the substratemark is formed by combining a plurality of oblique sections.

With this structure, it is possible to increase a number of types of thesubstrate mark and to assure the optical characteristic of thetransparent substrate in detail.

Further, in the mask blank according to this invention, the thin film isformed by a plurality of layers different in optical characteristic fromone another, and the shape of the film mark is determined by the opticalcharacteristics of these layers.

With this structure, it is possible to assure the opticalcharacteristics of a plurality of layers different in opticalcharacteristic and to prevent the deviation from specification due tothese optical characteristics.

Further, in the mask blank according to this invention, the thin filmincludes a halftone film and a light shielding film. The film markincludes a first film mark which is formed by the halftone film and asecond film mark which is formed by the light shielding film. The shapeof the first film mark is determined in accordance with an opticalcharacteristic of the halftone film and the shape of the second filmmark is determined in accordance with an optical characteristic of thelight shielding film.

With this structure, it is possible to individually assure the opticalcharacteristic of the halftone film and the optical characteristic ofthe light shielding film so that the mask blank has higher reliabilityin optical characteristic.

Further, in the mask blank according to this invention, the opticalcharacteristic is transmittance for an exposure wavelength and/orvariation of the transmittance in a thin film plane.

With this structure, it is possible to assure the transmittance for theexposure wavelength or the variation of the transmittance in the thinfilm plane and to prevent the deviation from specification caused by theabsorption of the exposure light by the transparent substrate itself,the production variation of the thin film, or the like.

Further, in the mask blank according to this invention, the exposurewavelength falls within a range between 140 nm and 200 nm.

With this structure, in a short wavelength region between 140 nm and 200nm in which large variation of transmittance is caused due to theabsorption of the exposure light by the transparent substrate itself andthe production variation of the thin film, or the like, it is possibleto assure the optical characteristic of the mask blank.

Further, in the mask blank according to this invention, a material ofthe transparent substrate is a synthetic quartz glass.

With this structure, even in the synthetic quartz glass in which thevariation of the optical characteristic occurs due to productionvariation, it is possible to obtain the mask blank having a highreliability in optical characteristic.

As described above, according to this invention, the substrate markhaving the shape determined in accordance with the opticalcharacteristic of the transparent substrate is formed on the cornerportion of the transparent substrate and, by this substrate mark, theoptical characteristic of the transparent substrate is assured. Thus, itis possible to prevent the deviation from specification of the maskblank due to the optical characteristic of the transparent substrate.

Moreover, if the film mark having the shape determined in accordancewith the optical characteristic of the thin film is formed on theperipheral portion of the thin film, the optical characteristic of thethin film is also assured. Thus, it is possible to prevent the deviationfrom specification by the synergistic effect of the opticalcharacteristic of the transparent substrate and the opticalcharacteristic of the thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a transparent substrate for a maskblank according to an embodiment of this invention;

FIG. 1B is an enlarged perspective view of a substrate mark in thetransparent substrate in FIG. 1A;

FIG. 1C is an enlarged perspective view of a conventional substratemark;

FIG. 2 is a diagram for explaining various shapes of the substrate markin FIG. 1B;

FIGS. 3 A through 3C are diagrams for explaining a thin film formed on amask blank;

FIG. 4A is a plan view showing a halftone film illustrated in FIG. 3A;

FIG. 4B is a plan view showing a light shielding film illustrated inFIG. 3A;

FIG. 5 is an enlarged perspective view of a characteristic part of FIG.3A:

FIG. 6 is a diagram for explaining various shapes of a first film markillustrated in FIG. 4A;

FIG. 7 is a diagram for explaining various shapes of a second film markillustrated in FIG. 4B;

FIG. 8 is a diagram for explaining a method for manufacturing atransparent substrate for a mask blank according to an embodiment ofthis invention;

FIG. 9 is a diagram for explaining a method for manufacturing a maskblank according to an embodiment of this invention;

FIG. 10 is a schematic view of a sputtering apparatus; and

FIG. 11 is a diagram showing a characteristic part of the sputteringapparatus in FIG. 10.

DESCRIPTION OF PREFERRED EMBODIMENT

Hereinafter, embodiments of this invention will be described withreference to the drawings.

(Transparent Substrate for Mask Blank)

Referring to FIGS. 1A through 1C and 2, description will be made of atransparent substrate for a mask blank according to an embodiment ofthis invention.

As shown in FIG. 1A, a transparent substrate 1 for a mask blank is arectangular glass substrate made of a synthetic quartz glass or thelike, and is formed by precisely polishing both principal surfacesthereof. On a predetermined corner portion of the transparent substrate1, a substrate mark M1 is formed by cutting off six surfaces (two sidesurfaces, one principal surface, one R surface and two chamferedsurfaces) into oblique sections.

Specifically, the substrate mark M1 is formed by shaping by the use of adiamond grindstone, followed by polishing into a mirror surface by usinga polishing cloth or a polishing brush.

The shape of the substrate mark M1 is determined in accordance with theoptical characteristic of the transparent substrate 1 (transmittance,variation of transmittance in a substrate plane, or the like). Forexample, the shape of the substrate mark M1 shown in FIG. 1B is appliedin case where the variation of the transmittance in the substrate planeat the exposure wavelength of 193 nm falls within the range of 90%±2%.

In this manner, it is possible to assure the optical characteristic ofthe transparent substrate 1 is based upon the shape of the substratemark M1.

As illustrated in FIG. 1B, the substrate mark M1 of this embodiment isformed by combining a plurality of (for example, 3) oblique sections, asis different from a conventional substrate mark shown in FIG. 1C. If thesubstrate mark M1 is formed in the above-mentioned manner, it ispossible not only to readily discriminate the transparent substrate 1from the conventional transparent substrate which is not assured inoptical characteristic but also to form a variety of substrate marks M1different in shape from one another by the shapes of the obliquesections and combinations thereof. For example, as shown in FIG. 2, if aplurality of shapes are determined for the substrate mark M1 and aplurality of values of the optical characteristic are related to theseshapes, respectively, it is possible to assure the opticalcharacteristic of the transparent substrate 1 in detail.

As the material of the transparent substrate 1 having a desiredtransmittance for the exposure light wavelength within the range between140 nm-200 nm, not only the synthetic quartz glass but alsofluorine-doped synthetic quartz glass, calcium fluoride, or the like maybe used.

(Mask Blank)

Subsequently, description will be made of a mask blank according to theembodiment of this invention with reference to FIG. 3A to 3C throughFIG. 7.

As illustrated in FIGS. 3A through 3C, the mask blank 2 is formed bydepositing a desired thin film, such as a halftone film 3 and a lightshielding film 4, on one principal surface (a principal surface oppositeto a surface provided with the substrate mark M1) of the transparentsubstrate 1. Accordingly, the mask blank 2 according to this inventionincludes a halftone type phase shift mask comprising a halftone film 3formed on the transparent substrate 1, a halftone type phase shift maskcomprising the halftone film 3 and the light shielding film 4 formed onthe transparent substrate 1, a photo mask blank comprising the lightshielding film 4 formed on the transparent substrate 1, and a substraterecessed type phase shift mask blank (substrate etched type phase shiftmask blank or quartz etched type phase shift mask blank). Alternatively,the mask blank 2 may be a mask blank comprising a resist film formed onthe thin film.

Further, this invention is particularly effective for a mask blank foruse with an exposure light source of the wavelength region of 140 nm-200nm, such as a mask blank for ArF excimer laser exposure, a mask blankfor F2 excimer laser exposure, or the like.

FIG. 4A shows the halftone film 3 deposited on the principal surface ofthe transparent substrate 1. On a peripheral portion (corner portion) ofthe halftone film 3, a first film mark M2 is formed by a portion inwhich the halftone film 3 is not deposited. The shape of the film markM2 is determined in accordance with the optical characteristic (thetransmittance, the variation of the transmittance in the halftone filmplane, the variation of the phase difference in the halftone film plane,or the like) of the halftone film 3. For example, the shape of the filmmark M2 shown in FIG. 4A is applied in case where the variation of thetransmittance of the halftone film 3 in the halftone film plane at theexposure wavelength of 193 nm is 6.0%±0.2% and the variation of thephase difference in the halftone film plane is 180°±3°. Thus, it ispossible to assure the optical characteristic of the halftone film 3 onthe basis of the shape of the film mark M2.

It is noted here that the shape or the type of the film mark M2 can beselected as desired. For example, as illustrated in FIG. 6, a pluralityof shapes are determined for the film mark M2 and various values of theoptical characteristic are related to these shapes, respectively. Inthis manner, it is possible to assure the optical characteristic of thehalftone film 3 in detail.

The FIG. 4B shows an antireflection light shielding film 4 deposited onthe halftone film 3. On a peripheral portion (corner portion) of thelight shielding film 4 formed on one principal surface, a second filmmark M3 is formed by a portion in which the light shielding film 4 isnot deposited. The shape of the film mark M3 is determined in accordancewith the optical characteristic (the variation of the reflectance of inthe light shielding film plane, the variation of the transmittance inthe light shielding film plane, or the like) of the light shielding film4. For example, the shape of the film mark M3 shown in FIG. 4B isapplied in case where the variation of the transmittance of the lightshielding film 4 in the light shielding film plane at the exposurewavelength of 193 nm is 3.0±0.1 in O.D. (optical density). Thus, it ispossible to assure the optical characteristic of the light shieldingfilm 4 on the basis of the shape of the film mark M3.

It is noted here that the shape or the type of the film mark M3 can beselected as desired. For example, as illustrated in FIG. 7, a pluralityof shapes are determined for the film mark M3 and various values of theoptical characteristic are related to these shapes. In this manner, itis possible to assure the optical characteristic of the light shieldingfilm 4 in detail.

FIG. 5 shows an example of assuring a variety of optical characteristics(the variation of the transmittance in the halftone film plane, thevariation of the phase difference in the halftone film plane, thevariation of the transmittance in the light shielding film plane, or thelike) of the mask blank 2 (the halftone type phase shift mask blank).Specifically, the optical characteristic of the thin film deposited onthe transparent substrate 1 is assured by the shape of the film mark M2formed on the peripheral portion of the halftone film 3 and the filmmark M3 formed on the peripheral portion of the light shielding film 4.Further, the optical characteristic of the transparent substrate 1 isassured by the shape of the substrate mark M1 formed on the transparentsubstrate 1.

It is noted here that each of the film marks M2 and M3 may be formed atany position or positions among the four corner portions of thetransparent substrate 1. Further, the optical characteristic of the thinfilm may be assured by the positions of the film marks M2 and M3 or acombination of the shape of the film mark and the position or positionsof the film marks.

Further, the film shape on the corner portion can be confirmed from theside of the transparent substrate (namely, the surface opposite to thefilm-deposited surface, i.e., the surface provided with the substratemark) with respect to the film mark M2 and from the surface of the lightshielding film with respect to the film mark M3.

(Method of Manufacturing a Transparent Substrate for a Mask Blank)

Next, description will be made of a method of manufacturing (supplying)the transparent substrate for a mask blank according to an embodiment ofthis invention with reference to FIG. 8. In the following, thetransparent substrate will be explained as the synthetic quartz glass.

(Step 1-a)

By the use of the known production method (for example, the productionmethod disclosed in Japanese Unexamined Patent Application Publication(JP-A) No. 8-31723 or Japanese Unexamined Patent Application Publication(JP-A) No.2003-81654), a synthetic quartz glass ingot is produced and iscut into a predetermined substrate dimension (for example, 152 mm×152mm×6.5 mm) to thereby produce a synthetic quartz glass plate.

(Step 1-b)

Then, the synthetic quartz glass plate is subjected to chamfering, andthe surfaces (containing both principal surfaces) of the syntheticquartz glass plate are precisely polished.

(Step 1-c)

Next, light from a deuterium lamp (wavelength of 193 mm) is irradiatedto nine positions of the polished one principal surface and thetransmittance (the transmittance variation) in the substrate plane ismeasured. Herein, the measurement of the transmittance is, performed,for example, by the use of a spectrophotometer (U-4100 manufactured byHitachi, Ltd.). The transmittance is calculated from the differencebetween input light amount of inspection light and output light amountthereof.

Herein, in-plane variation of the optical characteristic (transmittance)required for the mask blank for exposure by the ArF excimer laser andin-plane variation of the transmittance required for the transparentsubstrate (specification of the transparent substrate for the maskblank) taking the variation of transmittance in the thin film plane intoaccount are set to 90%±2%.

(Step 1-d)

Then, for the transparent substrate in which the variation of thetransmittance in the transparent substrate plane is 90%±2%, thesubstrate mark (the substrate mark shown in FIG. 1B) for assuring thevariation of the transmittance in the substrate plane is formed at onediagonal position on one principal surface of the transparent substrate.The substrate mark is formed by cutting off six surfaces (including theprincipal surface, two edge surfaces, one R surface, and two chamferedsurfaces forming the corner portion) into the oblique sections. In thismanner, by forming the substrate mark having the shape in accordancewith the optical characteristic of the transparent substrate, it ispossible to assure the variation of the transmittance in the transparentsubstrate plane. Further, by forming the substrate mark at one diagonalposition on one principal surface, it is possible to show that thesubstrate is the synthetic quartz glass.

(Step 1-e)

Subsequently, the surface (including both principal surfaces) of thetransparent substrate is precisely polished again to thereby obtain thetransparent substrate for a mask blank assured in optical characteristic(transmittance variation in the substrate plane).

A plurality of the transparent substrates for a mask blank thus obtainedare contained in a known glass substrate holder (for example, disclosedin Japanese Unexamined Patent Application Publication (JP-A) No.2003-264225), and supplied to a mask blank manufacturing departmentwhere the mask blanks are manufactured.

Although no description is made in the foregoing, a cleaning processstep may be appropriately carried out. In the foregoing description,after measuring the transmittance in the transparent substrate plane,the surface of the transparent substrate is precisely polished again inthe step 1-e. Alternatively, the transparent substrate for a mask blankmay be supplied to the mask blank manufacturing department withoutperforming the step 1-e.

(Method of Manufacturing the Mask Blank)

Next, description will be made of a method of manufacturing (supplying)a mask blank according to an embodiment of this invention with referenceto FIG. 9 through FIG. 11.

(Step 2-a)

By using the aforementioned transparent substrate for a mask blankassured in optical characteristic (transmittance variation in thesubstrate plane), the thin film (the halftone film) to become the maskpattern is formed by sputtering on the principal surface opposite to thesurface provided with the substrate mark. The deposition of the halftonefilm is preferably carried out by the use of a sputtering apparatushaving the following structure in order to suppress the transmittancevariation in the halftone film plane and the variation of the phasedifference in the halftone film plane.

As illustrated in FIG. 10, the sputtering apparatus has a vacuum chamber11. In the vacuum chamber 11, a magnetron cathode 12 and a substrateholder 13 are arranged. A sputtering target 15 adhered to a backingplate 14 is mounted to the magnetron cathode 12. The backing plate 14 isdirectly or indirectly cooled by a water-cooling mechanism. Themagnetron cathode 12, the backing plate 14 and the sputtering target 15are electrically connected to one another. On the substrate holder 13,the transparent substrate 1 is placed.

As shown in FIG. 11, the sputtering target 15 and the transparentsubstrate 1 are arranged so that confronting surfaces form apredetermined angle. In this case, an offset distance (for example, 340mm) between the sputtering target 15 and the transparent substrate 1, atarget-to-substrate vertical distance (for example, 380 mm), and atarget inclination angle ( for example, 15°) are appropriatelydetermined.

The vacuum chamber 11 is exhausted via a discharge port 16 by a vacuumpump. After an atmosphere inside the vacuum chamber 11 reaches such avacuum degree that does not affect the characteristic of the film to beformed, a mixed gas containing nitrogen is introduced from a gas inletport 17. Then, sputtering is carried out by applying a negative voltageto the magnetron cathode 12 by the use of a DC power source 18. The DCpower source 18 has an arc detection function so as to monitor adischarge state during sputtering. The pressure inside of the vacuumchamber 11 is measured by a pressure gauge 19. The transmittance of thehalftone film formed on the transparent substrate is adjusted by speciesand a mixing ratio of gases introduced through the gas inlet port 17. Incase of the mixed gas of argon and nitrogen, the transmittance isincreased by increasing the ratio of nitrogen. In case where a desiredtransmittance is not obtained only by adjusting the ratio of nitrogen,it is possible to further increase the transmittance by adding oxygeninto the mixed gas containing nitrogen. The phase angle of the halftonefilm is adjusted by a sputtering time so that the phase angle at theexposure wavelength is adjusted to about 180°.

The optical characteristic (the variation of the transmittance, thevariation of the phase difference, or the like) of the halftone film issubstantially assured by the deposition method. Therefore, the firstfilm mark assuring the optical characteristic of the halftone film isformed simultaneously with the sputtering deposition of the half tonefilm. Specifically, the halftone film is deposited by sputtering in thestate where the peripheral portion of the substrate is shielded so as toprevent deposition thereat. Thus, a portion without the halftone film isformed at the peripheral portion of the transparent substrate to serveas the first film mark.

(Step 2-b)

Then, light from a deuterium lamp (wavelength of 193 nm) is irradiatedto nine positions of the principal surface of the transparent substratewith the halftone film on the side of the halftone film and thetransmittance (the variation of the transmittance) in the halftone filmplane and the phase difference (the variation of the phase difference)in the halftone film plane are measured. Herein, the measurement of thetransmittance may be carried out by the use of the spectrophotometer(U-4100 manufactured by Hitachi, Ltd.) while the measurement of thephase difference is carried out by the use of a phase differencemeasuring instrument (MPM-193 manufactured by Lasertec Corporation).

Herein, the variation of the optical characteristic in the halftone filmplane required for the mask blank for the ArF excimer laser exposure is6.0%±0.2% and 180°±3° with respect to the transmittance and the phasedifference, respectively. Therefore, it has been confirmed whether ornot these specifications are satisfied.

(Step 2-c)

Subsequently, on the halftone film, the light shielding film isdeposited by sputtering. The deposition of the light shielding film ispreferably performed by the use of the sputtering apparatus same as thatmentioned above in order to suppress the variation of the opticalcharacteristic (the variation of the transmittance in the lightshielding film plane).

Since the optical characteristic (the variation of the transmittance inthe light shielding film plane) is substantially assured by thedeposition method, the second film mark assuring the opticalcharacteristic of the light shielding film is formed simultaneously withthe sputtering deposition of the light shielding film. Specifically, thelight shielding film is deposited by sputtering in the state where thefour corner portions of the substrate is shielded so as to preventdeposition thereat. In this manner, portions without the light shieldingfilm are formed on the corner portions of the transparent substrate toserve as the second film mark.

(Step 2-d)

Then, light from a deuterium lamp (wavelength of 193 nm) is irradiatedto nine positions of the surface of the light shielding film in thetransparent substrate with the light shielding film, and thetransmittance (the variation of the transmittance) in the lightshielding film plane is measured. Herein, the measurement of thetransmittance may be carried out by the use of the spectrophotometer(U-4100 manufactured by Hitachi, Ltd.)

Herein, the in-plane variation of the optical characteristic(transmittance) required for the mask blank for the ArF excimer laserexposure is 3.0±0.1 in O.D. (optical density). Therefore, it has beenconformed whether or not this specification is satisfied.

(Step 2-e)

Next, after applying a resist on the surface of the light shieldingfilm, heat treatment is carried out to form the resist film. Thus, themask blank (the halftone type phase shift mask blank) is obtained. Themask blank thus obtained is assured in optical characteristic (thetransmittance variation in the halftone film plane of 6.0%±0.2%, thephase difference variation in the halftone film plane of 180°±3°, thetransmittance variation in the light shielding film plane of 20%±2%) bythe shape of the substrate mark, the shape of the film mark of thehalftone film and the shape of the film mark of the light shieldingfilm.

A plurality of the mask blanks thus obtained are contained in a knownblank container (for example, as disclosed in Japanese Examined PatentApplication Publication (JP-B) No. 1-39653), and are supplied to a maskmanufacturing department where masks are manufactured.

EXAMPLES AND COMPARATIVE EXAMPLES

Hereinafter, with reference to examples and comparative examples,description will be specifically made of the transparent substrate for amask blank according to this invention.

Example 1

With respect to a synthetic quartz glass substrate of 152.4 mm×152.4mm×6.35 mm whose surfaces were precisely polished, the transmittance inthe substrate plane was measured, and the synthetic quartz glasssubstrate in which the transmittance variation fell within the range of90%±2% was prepared. Herein, on the synthetic quartz glass substrate,the substrate mark shown in FIG. 1B was formed at one corner portion ofthe synthetic quartz glass substrate so as to assure the variation ofthe transmittance in the substrate plane at the exposure wavelength of193 nm.

Then, by using the aforementioned sputtering apparatus, halftone typeshift mask blanks for the ArF excimer laser exposure, 100 in number,were manufactured.

Specifically by the use of a mixed target (Mo:Si=8:92 mol %) ofmolybdenum (Mo) and silicon (Si), the halftone film (the film thicknessof about 67 nm) made of molybdenum and silicon and nitrided was formedon the synthetic glass substrate by reactive sputtering (DC sputtering)under a mixed gas atmosphere (Ar:N₂=10%:90%, the pressure: 0.1 Pa) ofargon (Ar) and nitrogen (N₂). It is noted here that the halftone filmhad the film composition of Mo:Si:N=7:45:48.

Further, upon deposition by sputtering, a part of the synthetic quartzglass substrate was covered by a shielding plate in an area of about 2mm from the edge of the deposition surface faced to the sputteringtarget. In this manner, the region without the halftone film was formedin the area of about 2 mm from the edge of the glass substrate tothereby obtain the first film mark shown in FIG. 4A.

By the method of the step 2-b, the transmittance variation and the phasedifference variation in the halftone film plane were measured for themanufactured 100 samples. As a result of the measurement, for all of the100 samples, the transmittance variation in the halftone film plane was6.0%±0.2% while the phase difference variation in the halftone filmplane was 180°+3°. Thus, it was confirmed that the specifications weresatisfied.

Subsequently, after applying a resist by the use of a spin coatingapparatus, heat treatment was carried out to form a resist film havingthe film thickness of 400 nm on the halftone film. Thus, the halftonetype phase shift mask blank was obtained.

The halftone type phase shift mask blanks, 100 in number, thus obtainedsatisfied the transmittance variation of 6.0%±0.2% in the thin filmplane and the phase difference variation of 180°±3° in the thin filmplane as the specifications by the shape of the substrate mark and theshape of the film mark of the halftone film.

Example 2

With respect to a synthetic quartz glass substrate of 152.4 mm×152.4mm×6.35 mm whose surfaces were precisely polished, the transmittance inthe substrate plane was measured, and the synthetic quartz glasssubstrate in which the transmittance variation fell within the range of90%±2% was prepared. Herein, on the synthetic quartz glass substrate,the substrate mark shown in FIG. 1B was formed at one corner portion ofthe synthetic quartz glass substrate so as to assure the variation ofthe transmittance in the substrate plane at the exposure wavelength of193 nm.

Then, by using the aforementioned sputtering apparatus, halftone typeshift mask blanks for the ArF excimer laser exposure, 100 in number,were manufactured.

Specifically by the use of a mixed target (Mo:Si=8:92 mol %) ofmolybdenum (Mo) and silicon (Si), the halftone film (the film thicknessof about 67 nm) made of molybdenum and silicon and nitrided was formedon the synthetic glass substrate by reactive sputtering (DC sputtering)under a mixed gas atmosphere (Ar:N₂=10%:90%, the pressure: 0.1 Pa) ofargon (Ar) and nitrogen (N₂). It is noted here that the halftone filmhad the film composition of Mo:Si:N=7:45:48.

Further, upon deposition by sputtering, a part of the synthetic quartzglass substrate was covered by a shielding plate in an area of about 2mm from the edge of the deposition surface faced to the sputteringtarget. In this manner, the region without the halftone film was formedin the area of about 2 mm from the edge of the glass substrate tothereby obtain the first film mark shown in FIG. 4A.

By the method of the step 2-b, the transmittance variation and the phasedifference variation in the halftone film plane were measured for themanufactured 100 samples. As a result of the measurement, thetransmittance variation in the halftone film plane was 6.0%±0.2% whilethe phase variation in the halftone film plane was 180°±3°. Thus, it wasconfirmed that the specifications were satisfied.

Then, by using the aforementioned sputtering apparatus, the lightshielding film was formed on the halftone film.

Specifically, using a chromium (Cr) target, the chromium nitride film(the film thickness of about 15 nm) was formed on the synthetic quartzglass substrate by reactive sputtering (DC sputtering) under a mixed gasatmosphere (Ar:80%, N₂:20%, the pressure: 0.1 Pa) of argon (Ar) andnitrogen (N₂). It is noted here that the chromium nitride film has thefilm composition of Cr:N=80:20.

Next, using a chromium target, a chromium carbide film (the filmthickness of about 20 nm) was formed by reactive sputtering (DCsputtering) under a mixed gas atmosphere (Ar:CH₄=95%:5%, the pressure:0.1 Pa) of argon (Ar) and methane (CH₄). It is noted here that thechromium carbide film had the film composition of Cr:C=94:6.

Then, using the chromium target, a chromium oxide nitride film (the filmthickness of about 20 nm) was formed by reactive sputtering (DCsputtering) under a mixed gas atmosphere (Ar:NO=85.5%:14.5%, thepressure: 0.1 Pa) of argon (Ar) and nitrogen monoxide (NO). It is notedhere that the chromium oxide nitride film had the film composition ofCr:O:N=45:30:25.

Further, upon deposition by sputtering, four corner portions of thedeposition surface of the synthetic quartz glass substrate which isfaced to the sputtering target were covered with a shielding plate of aright triangle shape (one side having the length of about 6 mm, with atriangle notch formed at one position at the center of a side faced to aright angle). In this manner, the region without the light shieldingfilm was formed in the area of about 6 mm as the length of the sidesandwiching the right angle was formed at each of four corner portionsof the glass substrate to thereby obtain the second film mark shown inFIG. 4B.

By the method of the step 2-d, the transmittance variation in the lightshielding film plane was measured for 100 samples prepared. As a resultof the measurement, the transmittance was 3.0±0.1 in O.D. (opticaldensity). Thus, it was confirmed that the specification was satisfied.

Subsequently, after applying a resist by the use of the spin coatingapparatus, heat treatment was carried out to form a resist film havingthe film thickness of 400 nm on the halftone film. Thus, the halftonetype phase shift mask blank was obtained.

The halftone type phase shift mask blanks, 100 in number, thus obtainedsatisfied the transmittance variation of 6.0%±0.2% in the halftone filmplane, the phase difference variation of 180°±3° in the halftone filmplane and the transmittance variation of O.D. of 3.0±0.1 in the lightshielding film plane as the specifications by the shape of the substratemark, the shape of the film mark of the halftone film and the shape ofthe film mark of the light shielding film.

Comparative Example

A conventional synthetic quartz glass substrate (a glass plate providedwith a substrate mark to discriminate glass species of the glasssubstrate) assured in transmittance of a predetermined level or higherwas subjected to precision polishing of its surfaces and the syntheticquartz glass substrate of 152.4 mm×152.4 mm×6.35 mm was prepared.Herein, on the synthetic quartz glass substrate, the substrate markhaving the shape shown in FIG. 1C was formed.

Then, in the manner similar to the example 1, halftone type phase shiftmask blanks for the ArF excimer laser exposure, 100 in number, weremanufactured by using the aforementioned sputtering apparatus.

By the method of the step 2-b, the transmittance variation and the phasedifference variation were measured with respect to 100 samples thusmanufactured. As a result of the measurement, 94 among 100 samplessatisfied the specification including the transmittance variation of6.0%±0.2% and the phase difference variation of 180°±3°. 6 samples weredeviated from the specification.

With respect to 6 films deviated from the specification, the halftonefilm was peeled off from the synthetic quartz glass substrate, andthereafter the substrate was polished again. Then, the transmittancevariation of the synthetic quarts glass substrate in the substrate planewas measured. As a result, it was confirmed that the transmittance wasvaried within the range of 90%±10%.

Thus, in case where the halftone type phase shift mask blank for the ArFexcimer laser exposure was manufactured by the use of the glasssubstrate which was not assured in transmittance variation in thesynthetic quartz glass substrate plane for the exposure wavelength,those mask blanks which did not satisfy the specification were obtainedat a certain rate. However, as in the examples, in case where use wasmade of the glass substrate assured in transmittance variation in thesynthetic quartz glass substrate plane, all of the manufactured maskblanks satisfied the specification.

With respect to the 94 glass substrates with the halftone films, it wasconfirmed that the mask blanks satisfied the specification. Therefore,if the halftone film formed on the glass substrate is removed to formthe first film mark by irradiating the laser light to four cornerportions of the substrate, it is possible to assure the opticalcharacteristic (the transmittance variation in the halftone film planeand the phase difference variation in the halftone film plane) of themask blank.

Thus, the film mark may be formed by removing a specific region afterthe deposition other than simultaneous formation with the deposition asdescribed in connection with the above-mentioned examples. For example,use may be made of a method of removing the specific region by laserlight, a method of removing the specific region by utilizing an etchingprocess, or a method of removing the specific region by contacting afine probe or the like. In case where the removal is carried out afterthe deposition, the film mark may be formed after the opticalcharacteristic of the thin film formed on the transparent substrate ismeasured and it is confirmed that the predetermined specification issatisfied.

This invention is applicable to the transparent substrate for a maskblank and the mask blank. In particular, this invention is useful forthe mask blank for use with the ArF excimer laser or the F2 excimerlaser as the exposure light source and can prevent the deviation fromthe specification due to the variation of the optical characteristic.

While this invention has thus far been disclosed in conjunction with afew embodiments and examples thereof, it will be readily possible forthose skilled in the art to put this invention into practice in variousother manners.

1. A transparent substrate for a mask blank, which is required to have apredetermined optical characteristic, comprising: a substrate markformed by cutting off a predetermined corner portion into an obliquecross section, the substrate mark having a shape determined inaccordance with the optical characteristic.
 2. A transparent substrateas claimed in claim 1, wherein: the substrate mark is formed bycombining a plurality of oblique sections.
 3. A transparent substrate asclaimed in claim 1, wherein: the optical characteristic is transmittancefor an exposure wavelength and/or variation of transmittance in asubstrate plane.
 4. A transparent substrate as claimed in claim 1,wherein: the exposure wavelength falls within a range between 140 nm and200 nm.
 5. A transparent substrate as claimed in claim 1, wherein: amaterial of the transparent substrate is a synthetic quartz glass.